Skin is an outer membrane covering the outer surface of human body. As a primary barrier, it plays an important role in protecting and regulating internal organs and external body organs by performing various physiological functions that protect the body from various environmental factors including external stimuli, bathers, dryness, etc. Histologically, when a vertically dissected skin is observed under a microscope, it reveals three primary layers, an epidermis consisting of epithelial tissues, a dermis consisting of connective tissues, and hypodermis consisting of subcutaneous tissues, and each type of tissues exhibits unique physiological functions and has an interactive relationship.
Among these tissues, the connective tissue mainly consists of elastins and collagen fibers, and collagen plays a key role in maintaining the structure of the dermis layer of the skin. Collagen present in the dermis layer accounts for most of the extracellular matrix. Collagen is known to have a functional diversity capable of maintaining the mechanical firmness of skin, strengthening the cohesion of connective tissues and their resistance, supporting cell adhesion, inducing cell division and differentiation, etc. Glycoproteins, such as collagens, elastins, proteoglycans, fibronentins, and lamins, which constitute the extracellular matrix of the dermis layer are mainly produced in fibroblasts and secreted out of the cell. In addition, all nutrients and metabolic wastes are transported and metabolized through the extracellular space. The glycoproteins are involved in numerous cell-surface reactions, and help the skin maintain its elasticity and prevent generation of wrinkles by retaining a large amount of water in the extracellular matrix (Ko, J. H., Lee, S. J., and Lim, K. T., Toxicol. In Vitro, 19, 353, 2005; Cho, W. G., Kyung K. Y., and Yu, S. M., J. of the Korean Chemists, Soc., 26(2), 191, 2009).
Also, the degree of skin-moisturizing, which is considered as an important factor in various industrial fields such as cosmetics, dermatology, and medicine, and particularly, moisturization of cornified layers is directly associated with skin appearance (flexibility and roughness of skin), and becomes a barometer of one's physical condition. Further, the water content in the cornified layer influences the skin barrier homeostasis, which is related to the condition and permeability of skin, and thus the hygroscopicity of cosmetics or topical medications may vary. Therefore, skin moisturization is currently believed to be a crucial factor (Esposito E, Drechsler M, Mariani P, Sivieri E, Bozzini R, Montesi L, Menegatti E, Cortesi r, Int J Cosmet Sci, 29, p 39-47, 2007; Kasting G B, Barai N D, J Pharm Sci, 92, p 1624-31, 200).
Meanwhile, skin aging appears when both intrinsic aging (natural aging), which occurs naturally as people age, and actinic aging occur together. Both types of skin aging share common features of generation of wrinkles and reduction in the components that constitute the Langerhans cells, which are skin immune cells, and dermal cells. The difference between the two lies in that the actinic aging is characterized by skin thickening and an increase in elastic fibers, whereas the intrinsic aging is characterized by skin thinning. A combination of both types of aging may lead to generation of wrinkles. Specifically, on the one hand, as skin tissues age, the human skin fibroblasts present in the dermis layer of the skin also age, and as a consequence, the ability of producing fibers and substrates by the skin is reduced. Subsequently, the overall amount of substrates is reduced, the skin becomes thinned and skin elasticity is deteriorated, thereby forming wrinkles. Alternatively, the skin aging may accelerate wrinkle generation by attacking collagens and fibers, which are responsible for maintaining elasticity of moist, soft, and flexible skin, induced by free radicals and reactive oxygen species (ROS) produced by exposure to ultraviolet radiation. Meanwhile, many studies have shown that, most skin aging occurs due to the exposure to the sun rather than the age-related natural aging. There is a report that more than 80% of wrinkles are generated by the exposure to the sun.
Farmers and fishermen's skins are the representative examples showing the effects of routine exposure to ultraviolet radiation. Their skins are characterized by roughness and deep wrinkles, and distinctive diamond-shaped wrinkles around the scruff of the neck, which is easily exposed to UV rays. Such changes are called the actinic aging, and are distinguished from the changes caused by natural aging. In addition, such symptoms are prominent in the facial area where it may be always exposed to UV rays.
Further, recently, an increasing amount of UV rays is reaching the surface of the earth due to the environmental pollutions, and more chances of being exposed to UV rays due to increasing leisure and outdoor activities, etc. Accordingly, a care to prevent wrinkle generation has become important.
Skin is influenced by UV rays, etc., especially in summer when people enjoy many outdoor activities. As a consequence, the skin becomes rough, and may have a thicker cornified layer and fine wrinkles in autumn. When the skin in this state is in direct contact with dry autumn air, the skin becomes rougher, and the number of fine wrinkles increases rapidly. Further, when winter comes, the drastically decreasing temperature reduces physical activity levels and blood circulation efficiency, which results in prolonging skin's metabolic cycle. Therefore, the skin becomes even rougher, and fine wrinkle generation is considerably accelerated. Furthermore, in order to protect the skin from cold air, the skin itself thickens the cornified layer which makes the skin rougher. Among different parts of skin, the skin having a direct contact with the outside may produce dead skin cells when the dryness is intensified, and become thicker and stiff to stand against the cold air.
Meanwhile, the skin is renewed about every 28 days, that is, the dead cells are raised up to the cornified layer as the new cells are produced, and this is known as cell turn-over cycle. Skin aging begins in women aged 25. The skin aging occurs when the cell turn-over cycle takes longer for various reasons with skin problems (skin troubles), darkening skin tone, reduced skin moisture retention capacity, and finally fine wrinkles. Specifically, the skin becomes rougher and drier inbetween seasons because cold, dry air takes away a large amount of moisture in skin. Furthermore, the skin becomes even drier when the amount of secretion of sweat and sebaceum is dramatically reduced as the metabolic cycle slows down, which accounts for the increase in the dead skin cells on the skin surface.
Due to various reasons mentioned above, the skin may be characterized by thickness in the cornified layer, rough skin, and a rapid increase in fine wrinkles, especially since the age of 25. At this point of time where there is a rapidly growing interest in skin care, there is a desperate need for cosmetics capable of improving such rough skins and fine wrinkles. Specifically, external skin applications such as cosmetics exhibiting superior effects of improving rough skins and fine wrinkles, and simultaneously, confirming safety so that customers can safely use without hesitation are needed.
Thus, various methods for skin moisturization and skin wrinkle improvement have been suggested. For example, extensive studies on skin aging have been developed focusing on the functions that collagens play in the skin to improve the skin wrinkles, and thus, cosmetics containing collagens have become commercially available. However, the cosmetics mixed containing collagen are used by spreading collagen onto the surface of skin, and collagen, which is a polymer, is hardly absorbed into the percutaneous layer, thus unabling to perform its function. Therefore, the effect of wrinkle improvement is insignificant.
Further, there are a few existing substances which are known as collagen synthesis facilitating agents such as retinoic acid, transforming growth factor (TGF, tumor growth factor: Cardinale G. et al., Adv. Enzymol., 41, p. 425, 1974), animal placenta-derived protein (JP 8-231370), betulinic acid (JP 8-208424), and chlorella extract (JP 9-40823, JP 10-36283, a fibroblast growth facilitator), etc. However, their application to the skin makes limitation to the usage amount because of safety issues relating to irritation and rubefaction, and their effects are insignificant, and thus, it is difficult to expect substantial effects of skin improving functions. Accordingly, there is a need to develop an external skin application having a superior wrinkle improvement effect which is safe when applied onto skin.
Under the above circumstances, the present inventors endeavored to study a material having superior skin moisturizing and wrinkle improving effects which is safe to skin, and completed the present invention upon confirming that, when a compound represented by Formula 1 obtained from Anemarrhena asphodeloides Bunge was spread onto skins of animal models, the compound improved skin damage of skin bather suppressing the skin damage, thereby alleviating the depth and length of wrinkles, etc.